The present invention relates to image forming apparatuses such as an electrostatic recording apparatus and electrophotographic apparatus, a method for forming an image, and developing agents for use in the apparatuses and method.
Presently, a high image quality of a color copying machine and printer is an essential factor. To improve the image quality, toner characteristics required to be improved are particle diameter, charging properties, toner shape, and the like. Of these characteristics, the particle diameter is particularly important. As the particle diameter of toner decreases, the reproducibility of dots and thin lines improves.
A polymerization method and pulverization method are examples of a toner manufacturing method. Of these methods, the pulverization method is generally used because the cost is low. However, when this pulverization method is used, the manufacturing cost increases as the particle diameter of toner decreases. A polyester-based resin often used in color toner has high affinity for paper and hence is advantageous in fixing properties, but has the disadvantages that, because the resin is hard, the pulverization time prolongs and the yield worsens. Therefore, this polyester-based resin is inferior in pulverization efficiency to a styrene-acryl-based resin normally used in monochrome toner.
In addition, the material of monochrome toner is relatively inexpensive since an inexpensive coloring agent called carbon black is used. In contrast, the materials of color toners are expensive because expensive yellow, magenta, and cyan pigments are used. A yellow pigment usable in toner is particularly expensive.
Also, the offset properties and transparency of color toner are very important because colors are overlaid on each other. Accordingly, a binder resin, wax, and the like of color toner are often required to have more functions than required of monochrome toner. Furthermore, to improve the dispersibility of a color pigment with respect to a binder resin in a kneading process, it has been demanded to further improve the dispersion technique.
As described above, the material cost and manufacturing cost of color toner are inevitably higher than those of monochrome toner, and this increases the cost of the final product.